1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor device, and more particularly to a method of protecting a wafer backside during electroless plating and dicing the plated wafer into individual dies.
2. Description of Related Art
Electroless nickel plating and immersion gold processes are widely used to deposit Ni/Au coating onto aluminum alloy pads on the front sides of wafers without the need for masks or electric plating current. It is a cost effective approach that provides a hard layer for copper wire bonding and a solder wettable layer and diffusion barrier for clip bonding and flip chip packaging.
During electroless nickel plating, the back side of a wafer needs to be covered with an insulation layer to avoid nickel plating, usually with poor adhesion, on this region. The unwanted plating consumes nickel and decreases the lifetime of the plating bath. Furthermore, if incoming wafers have metal layers such as silver on back sides thereof, corrosion of the back metal and contamination of the plating chemicals occurs. A resist layer is typically used to protect the back surface of the wafer. However, this approach necessarily involves a resist applying process and a resist stripping process. The latter process may include additional cleaning steps to remove residues of the resist. The complex process lowers production throughput and increases total cost.
In another approach, a temporary protection tape can be applied on the back side of a wafer before electroless plating. However the tape adhesive is usually poor in chemical resistance and may cause serious tape detachment problems at circumferential areas of the wafer as well as contamination of the plating chemicals. Additionally, the extra steps of tape application and removal increase cost and the chance of wafer splitting or cracking, especially for relatively thin wafers.
There is therefore a need in the art for a method of fabricating a semiconductor device employing electroless plating that overcomes the disadvantages of the prior art. The method preferably provides for a simple process with good protection, high throughput and low cost.